Manufacture of vanillin



Patented May 27, 1952 MANUFACTURE OF VANILLIN Eugene Wilhelm Schoeflel, Kronenwetter, Wis.,

assignor to Salvo Chemical Corporation, Rothschild, Wis., a corporationof Wisconsin.

No Drawing. Application -Mayl, 1950; Serial No. 160,089

12 Claims. 1

This invention relates to a process for makin vanillin, particularly to a process for preparing vanillin from sulfite waste liquor.

It has long been known that digestion at elevated temperature of alkaline sulfite waste pulping liquor leads to the formation of small amounts of vanillin which can be recovered. in various Ways in the form of a pure product. These processes as heretofore practiced have led to the recovery of considerably less vanillin than 10% of the weight of the lignin used, usually from about 2 to about 5%.

Among the agents which-have been used to treat alkaline waste sulfite liquor in an attempt to develop a commercial process for the recovery of vanillin are included various oxidizing agents, such as nitrobenzene and air at moderately elevated temperatures and pressures. It has been generally concluded by past workers in this field, as for example Patent 2,434,626 January 13, 1948, that optimum conditions for the preparation of vanillin from alkaline waste sulfite liquor should avoid the use of temperatures much above 150 to 180 C. and of pressures of atmospheric oxygen of more than about atmospheres. Under such conditions vanillin has been produced on a small scale but in low yield as previously mentioned.

It has now been found, and is herein first disclosed as my inventicnjthat, contrary to expectation, the yield of vanillin obtained by treating liquors containing lignin in solution, such as waste liquors derived from wood pulping processes, such as waste sufite liquor, made alkaline with a suitable amount of an alkaline.

metal substance, such as an alkali metal hydroxide, for example caustic soda, with atmospheric oxygen is increased greatly by using temperatures and pressures considerably higher than those heretofore disclosed and by limiting the contact time of the hot liquor and oxygen or air to 10 minutes or less, generally to from about 0.5 to about 5 minutes. The contacting of the liquor and air is preferably carried out in such fashion that a large surface of the liquor is exposed to the action of the air, e. g., in a falling film type of apparatus. Under such conditions it has been found possible to obtain consistently a conversion and recovery of up to 18 to 22% by Weight of the lignin in the sulfite Waste liquor used as vanillin in the efliuent liquor from the contacting step. About 80%; of, the vanillin in the efiiuent liquor can be recovered by conventional procedures in the formv of pure crystalline vanillin suitable for use wherever the natural product has heretofore been used.

My process is generally-carried out by injecting orpumping the=alkaline waste sulfite liquor. or other lignincontaining liquor, andcompressed air or oxygen continuously into a heated reaction. zone'maintained at a temperature from about 200 C. to about 270 0., preferably at between about 225-and about 250 0., and under pressure-of 'above'about 1000 pounds per square inch, preferably between about 1250 and 2000 pounds per square inch.

The contacting vof the sulfite liquor with the air or oxygen is. carried out conveniently and advantageously and in continuous fashion. by utilizing a reactor or reaction vessel through which the liquor flows as a thin film and has a relatively large surface exposed to the air passing through the reactor. Heating is accomplishedin any convenient way, e. g., by immersing the reactor in a hot bath of oil or other liquid. Generally, the liquor or the air or both are heated prior to introduction into the reactor. Adiabatic compression of theair can be practiced if desired. Batch processing can be employed when convenient.

Gaseous products and oxidized liquor can be withdrawn continuously from the reactor, preferably at arate to cause the liquor to remain in the reaction zone for not to exceed about 10 minutes andusuall'y for between about 0.5 to about 5 minutes, it being apparent that the actual rate of flow through the reactorwill depend upon the amount of liquid maintained in the reactor. It will also'be-apparent that a considerable proportion of the reactor volume is generally filledjwith .gas rather than with liquid.

Thegaseous efil'uent from the reaction zone is found to be substantially free of elemental oxygen. The gaseous product is generally discarded but can be workedup' for recovery of nitrogen if desired. The oxidized liquor is cooled as rapidly as possible immediatelyupon being withdrawn from the reactor. This'is accomplished conveniently by reducing the pressure suddenly to atmospheric pressure to evaporate a part of the water and subsequently cooling the partially concentrated. product. to ordinary temperatures, e. g., to about- 25 to 30 C. vanillin can then be recovered from the. oxidized liquor in any convenient and. conventional manner. One convenient way consiststin extracting the vanillinfromthe processed.alkalinezliquor, with a water: immiscible alcohol, i. e.. n-butanol such as: describedin U..S'. :Patent 2,104,701 January 4. 1938, then obtaining the vanillin from the butanol extract by conventional means, or by the extraction procedure described in U. S. Patent 2,399,607 April 30, 1946 to Servis. Crude vanillin thus obtained can be purified by vacuum distillation and recrystallization. The sulfite liquor which is used in the process can comprise sulfite liquor from the pulping various species of wood, such as spruce, hemlock and balsam.

Sulfite liquor from deciduous woods, i. e., aspen or birch will also give vanillin by the process described, but simultaneously syringic aldehyde. Since these aldehydes are difficult to separate from each other, liquors from deciduous woods are less desirable as starting material for the described process if pure vanillin is the required end product.

Any liquors containing lignin are useable in the process. Thus sulfite waste liquors which have been processed for-utilizing the sugars contained therein, 1. -e., by fermentation to alcohol or for propagating yeast can be used. The lignosulfonate isolated from sulfite waste liquor by the procedure described in U. S. Re. 18,268 December 1, 1931 to Howard is also a suitable starting material. Black liquor from the kraft and soda process has also been used as a convenient starting material.

It has been found convenient to use liquor containing from about 25 to about 45 grams per liter of lignin and from about '75 to about 125 grams per liter of sodium hydroxide. Satisfactory results have been obtained using a liquor which contained 35 grams per liter of lignin and 100 grams per liter of sodium hydroxide, but considerable variation in the composition of the sulfite liquor can be tolerated in the process.

The proportion of atmospheric oxygen to sulfite liquor introduced into the reaction zone is generally maintained at between about 5 and about 40 liters of actual oxygen, measured under atmospheric conditions, per liter of liquor. Under such conditions, substantially all of the oxygen in the air is utilized within the reaction zone and a maximum yield of vanillin is obtained. The mechanism of the reaction whereby vanillin is formed is not clearly understood, but it has been noted that there is a decrease in the pH of the liquor upon its passage through the reactor. In a typical instance, given in the following example, the pH of the liquor fellirom 11.8 to 10.6 during its passage through the reactor.

Example sulfite waste liquor from 'a pulping process which was at pH 11.8 and which contained 35 grams per liter of lignin and 100 grams per liter of sodium hydroxide was pumped continuously into a reactor of several liters capacity. The reactor was immersed in an oil bath which was maintained at a temperature of about 200 C. and the pressure in the reactor was maintained at about 1500 pounds per square inch. Compressed air was also forced ,into the reactor and the liquor and air contacted intimately and thoroughly in the reactor.

sulfite liquor was passed through the reactor at the rate of 1'70 liters in 125 minutes and the volume of liquid in the reactor was maintained at 3 liters. The compressed air was forced into the reactor at the rate of 26.6 liters of actual oxygen, measured under atmospheric conditions, for each liter of sulfite liquor, pumped in. The reaction was somewhat exothermic and the efiluent 4 liquor from the reactor was at a temperature of 252 C.

Unreacted gaseous products and oxidized liquor were withdrawn continuously and separately from the reactor. The withdrawn gaseous products were substantially free from oxygen and the withdrawn liquid was at pH 10.6. The liquid was cooled and partially evaporated by flashing to atmospheric pressure and then further cooled rapidly to about 25 C. Assay of the liquid showed it to contain about 21 grams of vanillin for each grams of lignin contained in the alkaline sulfite liquor used. About 80 of the vanillin present in the oxidized liquor was recovered as substantially pure vanillin by the method described above.

It is to be understood that variations and modifications may be made in regard to the various details of my invention as herein disclosed which 1. The method for producing vanillin from a waste sulfite liquor made alkaline with an alka-' li metal hydroxide, which comprises subjecting the alkaline liquor to the action of oxygen at a temperature above about 200 C. and a pressure above about 1000 pounds per square inch for a time not exceeding about 10 minutes, rapidly cooling the treated liquor to about room temperature, and separating vanillin therefrom.

2. The method for producing vanillin from waste sulfite liquor made alkaline with an alkali metal hydroxide, which comprises subjecting the alkaline liquor to the action of air at a temperature above about 200 C. and a pressure above about 1000 pounds per square inch for a time not exceeding about 10 minutes, rapidly cooling the treated liquor to about room temperature, and separating vanillin therefrom.

3. The method of claim 1 wherein the alkaline waste sulfite liquor contains from about 25 to about 45 grams per liter of lignin and from about '75 to about grams per liter of sodium hydroxide.

4. The method of claim 1 wherein the alkaline waste sulfite liquor is subjected to the action of atmospheric oxygen at a temperature of between about 225 and about 250 C.

5. The method of claim 1 wherein the alkaline waste sulfite liquor is subjected to the action of atmospheric oxygen at a pressure between about 1250 and 2000 pounds per square inch.

6. The method of claim 1 wherein the alkaline waste sulfite liquor is subjected to the action of atmospheric oxygen at above about 200 C. for from about 0.5 to about 5 minutes.

7. The method for producing vanillin from waste sulfite liquor made alkaline with an alkali metal hydroxide, which comprises introducing the alkaline liquor continuously into a reaction zone maintained at a temperature of between about 225 and about 250 C. and under a pressure between about 1250 and about 2000 pounds per square inch, introducing oxygen continuously into the reaction zone at a rate between about 5 and about 40 liters of oxygen measured under atmospheric conditions per liter of alkaline liquor, withdrawing continuously treated liquor and unreacted gaseous components from the reaction zone, rapidly cooling the treated liquor to about room temperature, and separating vanillin from the cooled liquor.

8. The method of making vanillin from alkaline waste sulfite liquor containing about 25 to about 45 grams per liter of lignin and from about 75 to about 125 grams per liter of sodium hydroxide which comprises introducing the alkaline liquor continuously into a reaction zone maintained at a temperature of between about 225 and about 250 C. and under a pressure between about 1250 and about 2000' pounds per square inch, introducing oxygen continuously into the reaction zone at a rate between about 5 and about 40 liters of oxygen measured under atmospheric conditions per liter of alkaline liquor, withdrawing continuously treated liquor and unreacted gaseous components from the reaction zone, rapidly cooling the treated liquor to about room temperature, and separating vanillin from the cooled liquor.

9. The method of claim 7 wherein the alkaline waste sulfite liquor is introduced into the reaction zone and the treated liquor is withdrawn therefrom at rates to limit the contact time of the heated liquor with oxygen to from about 0.5 to about 5 minutes.

10. The method for producing vanillin from a liquor containing lignin made alkaline with an alkaline metal substance, which comprises subjecting the alkaline liquor to the action of oxygen at a temperature above about 200 C. and a pressure above about 1000 pounds per square inch for a time not exceeding about 10 minutes, rapidly cooling the treated liquor to about room temperature, and separating vanillin therefrom.

11. The method of claim 10 wherein the alkaline liquor is black liquor from the krait pulping process.

12. The method of claim 10 wherein the alkaline liquor is black liquor from the soda pulping process.

EUGENE WILI-IELM SCHOEFFEL.

REFERENGES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain Sept. 8, 1948 

1. THE METHOD FOR PRODUCING VANILLIN FROM WASTE SULFITE LIQUOR MADE ALKALINE WITH AN ALKALI METAL HYDROXIDE, WHICH COMPRISES SUBJECTING THE ALKALINE LIQUOR TO THE ACTON OF OXYGEN AT A TEMPERATURE ABOVE ABOUT 200* C. AND A PRESSURE ABOVE ABOUT 1000 POUNDS PER SQUARE INCH FOR A TIME NOT EXCEEDING ABOUT 10 MINUTES, RAPIDLY COOLING THE TREATED LIQUOR TO ABOUT ROOM TEMPERATURE, AND SEPARATING VANILLIN THEREFROM. 